My understanding of the Pro selection process is as follows:
Every year, the pros from the previous series who wish to return are interviewed by the producers.
In the meantime, auditions are held for dancers wishing to become SCD pros.
If the producers decide to drop any of the existing pros or pros have decided not to return themselves, they are replaced by auditionees.
We don't know if there are many (if any) british pros applying from this process. If there are then some of them may insist on being hired as a pair (like Erin/Anton, James/Ola, Vincent/Flavia come as a pair) or may not simply come up to scratch.
Sometimes auditionees can be unsuccessful in one country, but be spotted and recommended for another country's format (Tristan McManus being one example- auditioned here in 2010, turned down but recommended for dwts US).
Iveta has danced in the dwts Las Vegas show (produced by BBC world wide) and in another country's format of the show. She may have even auditioned for scd this year. Either way, she was known to the producers who have had to make a quick replacement.
Personally, i'm really chuffed that they've secured someone of her calibre & qualifications to appear & I've enjoyed looking up some of her dances on Youtube. I couldn't give a flying f*ck where someone is from if they are well qualified for the job they've been employed to do. I'm also amused/baffled at some of the moaning considering how much people usually moan at the lack of 10 dance specialists in SCD